1. Field of the Invention
The present invention relates to remote sensing of reservoir conditions during the production of hydrocarbons. More specifically, the invention relates to systems and methods for measuring and interpreting electric currents induced in liners (or casing) of production wells by electromagnetic sources located in adjacent unlined sections.
2. Description of the Related Art
During hydrocarbon production and management the occurrence of water breakthroughs, in particular during water injection, constitutes an undesirable event because of the drop of oil/water ratio and the extra costs that could be incurred to rehabilitate the affected production wells. The water breakthrough may also imply changes in the properties of the reservoir, such as wettability and relative permeability that might be difficult to revert. The formation of water-flooding paths connecting injector and production wells can bypass sweet spots in the reservoir, rendering the stimulated production ineffective and ultimately leading to the abandonment of affected production wells due to non-economical water/oil-cut levels. Current technology detects the water front when it has already reached the well (such as the in US Patent Application Pub. No.: 2008/0262735A1), or senses the approaching water fronts when they are at such small distance from the wellbore (for example, existing inductive electromagnetic well logging tools) that modifications of production variables cannot avoid undesired changes of the reservoir properties that already have taken place in the vicinity of the production wells and the adverse consequences and costs associated with the water breakthrough.
Current electromagnetic monitoring systems such as the ones disclosed in the US Patent Application Pub. No.: 2006/003857A1 or US Patent Application Pub. No.: 2009/0005994A1 use sensors or sources on the surface to monitor changes in the reservoir, but this reduces the detectability and discrimination of these techniques, and even when sources and receivers are proposed to be located in the well, no system published to date has proposed to measure the current induced in adjacent liners or casing as part of the receiver (detector) that sense the electromagnetic response of the subsurface.